1. Field of the Invention
The present invention relates to the improvement in the installation structure for a microwave oscillation circuit unit for use in a low noise converter for satellite broadcasting use or the like.
2. Description of the Prior Art
A microwave oscillation circuit unit is generally formed with the use of a metallic box internally provided with an oscillation circuit and is installed on a chassis base by means of specified screws.
FIGS. 1 and 2 and FIGS. 3 and 4 depict conventional installation structures of a microwave oscillation circuit unit.
In FIGS. 1 and 2, the microwave oscillation circuit unit 3 is installed on a lower surface of a chassis base 6, with an earth plate 9 interposed between them. The chassis base 6 is provided on its upper surface with a circuit substrate 7 having openings 8 for receiving therein respective washers 10 and nuts 11, which are threaded on the screws 1 and 2 of the unit 3. The unit 3 is fixedly mounted on the chassis base 6 by tightening the nuts 11. In this event, since the washer 10 are in abutment with the chassis base 6, torque caused by tightening the nuts 11 acts upon the chassis base 6.
On the other hand, in the structure shown in FIGS. 3 and 4, the washers 10 abut on the circuit substrate 7. Accordingly, the torque caused by tightening the nuts 11 acts upon the circuit substrate 7.
In both the structures of FIGS. 1 and 2 and FIGS. 3 and 4, a power supply terminal 4 and an output terminal 5 of the unit 3 are soldered to respective conductor patterns 12 and 13 formed on the circuit substrate 7.
In the structure of FIGS. 1 and 2, the torque control required for the proper tightening is not so difficult. However, since the circuit substrate 7 is not restricted by the tightening, it is very likely that the circuit substrate 7 would lift from the chassis base 6. This phenomenon takes place when a relatively soft circuit substrate, of for example Teflon, is subjected to deflection caused by heat treatment during a soldering process for chip components and the like. Such lifting is substantially rectified by depressing the circuit substrate 7, particularly in the vicinity of the terminals 4 and 5, or by providing additional tightening portions of the circuit substrate 7 to the chassis base 6, when the power supply terminal 4 and the output terminal 5 are soldered. Accordingly, this structure is disadvantageous due to such increased incidental work or in that circuit pattern design would be restricted to some extent.
On the other hand, the structure as shown in FIGS. 3 and 4 can practically prevent the lifting of the circuit substrate 7 from the chassis base 6 but cannot be applied to a chassis base 6 having thereon a soft circuit substrate of Teflon or the like. The reason for this is that torque control required for the proper tightening between the nuts 11 and the screws 1 and 2 is hardly possible with respect to the soft circuit substrate. Furthermore, the circuit substrate 7 is subject to shrinking under severe circumstances in which the change in temperature or humidity is relatively large. Accordingly, this structure cannot guarantee the proper tightening because the thickness of the circuit substrate 7 changes due to deterioration with age.
These drawbacks cause several problems. For example, the above described structure occasionally brings about a change in distributed capacitance, followed by a large fluctuation of an oscillation frequency, impossibility of effective supply of an oscillation output, large radiation of the oscillation output towards the outside or the like.